1. Field of the Invention
The present invention relates generally to systems and methods for treating liquids, such as wastewater, and more particularly to a wastewater treatment system and method capable of treating and covering wastewater contained in a treatment basin.
2. Discussion of Related Art
In liquid treatment facilities, such as a wastewater treatment facility, it is well known to provide an aerator or a mixer to stimulate wastewater contained in a treatment basin. Mixers provide desired mixing of the wastewater so as to stimulate biological material used to treat the wastewater. Aerators also mix the wastewater and provide the added feature of introducing oxygen into the wastewater. For the purposes of this disclosure, the term “aerator” will be used to describe both aerators and mixers, and other types of aeration devices, such as aspirating aerators, unless otherwise described separately. In such facilities, it is further well known to cover the wastewater basin to prevent birds from nesting in the wastewater basin, to reduce heat loss, to reduce odors emanating from the basin, and to control the growth of algae within the basin by reducing sunlight.
One issue in designing a cover is that the cover must be compatible with the aerator, which can be designed to float on the water's surface. Surface aerators have several advantages over submerged aerators, such as lower installed cost, quick and simple installation, and virtually no routine maintenance requirements. One disadvantage with such surface aerators is that cooling caused by operating in winter conditions, for example, can reduce the biological treatment efficiency. Another disadvantage is that surface aerators are often used in lagoon treatment processes having a large surface area, which can result in a long hydraulic retention time. This long retention time can lead to algae blooms, which in turn can lead to effluent TSS, BOD5, and turbidity. Thus, it is somewhat important to control or eliminate algae to optimize the overall treatment performance of the wastewater treatment system.
There is presently available a fiberglass cover that is an optional attachment for surface aerators to reduce heat loss as well as to control excessive misting and odors caused by the aerator spray. Specifically, this type of cover serves as a dome provided directly over the surface aerator to control mist and water flow resulting from the aerator water discharge. Such a cover, while effective in controlling the mist, is less effective in reducing heat loss in a basin having a long retention time. In addition, a domed cover does not provide algae control, nor does it prevent birds from nesting in the basin.
There are also commercially available polyester fabric covers that are effective in shading the surface. One disadvantage associated with such fabric covers is that the seams, which attach the fabric sheets to one another, are susceptible to degradation. Another disadvantage is that adequate space must be provided around the aerator to prevent the fabric cover from being ingested by the aerator during its operation.
Another water surface “cover” is provided in the form of hollow plastic balls that cover 90% of the water's surface. In one known application, each ball is fabricated from black, ultra violet-stabilized, high density polyethylene. The ball is 100 millimeters (four inches) in diameter, has a wall thickness of less than 1 mm, and weighs 40 grams. Each ball can be formed with an opening that is closed by a plug. This construction enables the ball to be filled with water for ballast and thereby prevent the ball from being blown out of the basin during windy conditions. One problem associated with this construction is that the balls, due to the susceptibility of the plugs becoming dislodged, will leak over time. This results in the sinking of the balls, and the inevitable result of being ingested by the aerator, thereby causing in damage to the aerator. Balls formed without a plug are extremely light and subject to being blown out of the basin.